I. Field of the Invention
The present invention relates to wireless communications. More particularly, the present invention relates to a novel and improved method and apparatus for performing transmit and admission control in a satellite based wireless communication system.
II. Description of the Related Art
FIG. 1 is a highly simplified diagram of a satellite based telecommunications system. Wireless satellite telecommunications systems are typically used to exchange between to remote points For example, credit verification information may be exchanged between the point of sale and a master credit history database using a wireless satellite telecommunications system.
During operation of the wireless satellite telecommunications system, earth bound terminals 50 exchange data messages with hub 52 via radio frequency signals relayed from satellite 54. The signals transmitted from hub 52 are referred to as the forward link and the signals transmitted from terminals 50 are referred as the reverse link. The use of a satellite allows remotely located terminals without line of sight access to communication with one another. Colocated terminal 51 is coupled to hub 52 and facilitates measurement of various characteristics about transmission channel to and from satellite 54.
Many satellites have been placed into geostationary orbit around the earth to implement satellite telecommunications systems. A geostationary orbit is one in which the satellite remains above the same location on the earth's surface at all times. In general, the geostationary satellites used to operate wireless satellite messaging systems are placed 2° apart in the sky to maximize the number of satellites available. This relatively close proximity can cause transmissions directed at one particular satellite to generate interference that is detected by adjacently located satellites. This is particularly true with the use of ultra-small aperture antennas (typically 18 inch), which focus the transmission to a reduced degree, but which are highly desirable because they can be conveniently placed in a greater number of locations. To ensure that each satellite operates properly, various governmental standards bodies limit the peek interference that a wireless system can generate to adjacent satellites.
This limitation on the peak interference makes it desirable to use code division multiple access (CDMA) signal processing techniques in a satellite communication system because CDMA signal processing spreads the RF energy transmitted across a larger amount of bandwidth than other data transmission technologies. Spreading the RF energy across a wider RF bandwidth reduces the energy density at any particular frequency, which is the way in which the peak energy level is generally measured. Thus, the use of CDMA signal processing allows a greater amount of energy to be transmitted, and therefore a greater number of communications to be conducted, while complying with international standards of operation. Thus, the use of CDMA signal processing facilities the use of ultra-small aperture antennas, which tend to “spill” power over to the next satellite more readily.
Other factors also must be considered when implementing a satellite based telecommunications system including the average amount of delay that for the transmission of data messages. Also it is desirable to operate a CDMA based satellite communications system as efficiently as possible, since RF bandwidth is a limited resource. Thus, the present invention is directed to performing transmit power control and admission control for a satellite based CDMA communication system that provides efficient use of the available RF bandwidth while transmitting data messages with acceptable delay, and which complies with Federal Communication Commission (FCC) regulations, as well as the regulations of other standards bodies, regarding interference with adjacent satellites when performed using ultra-small aperture antenna dishes.